Playing surface with a mixture of stones and elastic granules

ABSTRACT

Playing surface, in particular a sports floor or playing field. The playing surface comprises a substrate layer lying on top of a base layer and one or more additional layers lying on top of the substrate layer. The substrate layer is a leveled, compacted mixture of elastic granules and stones. At least one of the additional layers is an elastic layer. The substrate layer and the one or more additional layers form the playing surface.

FIELD OF THE INVENTION

The invention relates to playing surfaces, in particular sports floors and playgrounds and playing surfaces that provide robust protection against weather damage.

BACKGROUND AND RELATED ART

Playing surfaces such as sports floors (e.g., running tracks, tennis courts, artificial turf, etc.) and playground floors (e.g., floors used in leisure-time facilities) typically are elastic and have some shock-absorbing properties to prevent player injuries. A broad variety of playing surfaces exists.

US 2006/0084513 A1 (De Vries et al.) discloses a method for laying a playing field comprising a layer of a resilient and/or damping material and a top layer arranged on the resilient layer. The top layer may be a synthetic turf.

International patent application WO 2009/118388 A1 describes the forming of an elastic layer (e-layer) by mixing polymer granules with a polyurethane binder.

SUMMARY

The invention provides a method for laying a playing surface and for a corresponding playing surface as specified in the independent claims. Embodiments are given in the dependent claims. Embodiments and examples described herein can freely be combined if they are not mutually exclusive.

In one aspect, the invention relates to a method for laying a playing surface. The playing surface is in particular a sports floor or playing field. The method comprises the steps of:

-   -   providing a substrate mixture comprising elastic granules and         stones;     -   applying the substrate mixture on a base layer;     -   leveling the applied substrate mixture;     -   compacting the leveled substrate mixture such that a compact         substrate layer is formed; and     -   applying one or more additional layers on top of the substrate         layer, at least one of the additional layers being an elastic         layer, wherein the substrate layer and the one or more         additional layers form the playing surface.

This method of laying a playing surface may be particularly beneficial in temperate climate zones in which many freeze-thaw cycles are observed each year.

In a further aspect, the invention relates to a method for laying a playing surface that provides robust protection against freeze-thaw-cycle-induced damages. The playing surface being in particular a sports floor or playing field. The method comprises the following steps:

-   -   providing a substrate mixture comprising elastic granules and         stones;     -   applying the substrate mixture on a base layer, the base layer         being located in a geographic area subjected to multiple         freeze-thaw-cycles per year; for examples, in countries in         temperate climate zones like Canada or Germany, a playing         surface is typically subjected to multiple freeze-thaw-cycles         per year;     -   leveling the applied substrate mixture;     -   compacting the leveled substrate mixture such that a compact         substrate layer is formed; and     -   applying one or more additional layers on top of the substrate         layer, at least one of the additional layers being an elastic         layer, wherein the substrate layer and the one or more         additional layers form the playing surface.

Frequent freeze-thaw cycles damage the solid substrate (base layer) onto which a playing surface is placed. Larger cavities, in particular cracks and holes, are created by water that has managed to penetrate the base layer; because when water freezes to ice, it has a larger volume and may thus burst even concrete or stone over time. If a ball hits a sports floor that has been laid on an uneven base layer with larger cracks or holes, or if these holes have developed later because the base layer has aged over many years of use, the ball (or any other object hitting the ground) can damage the sports floor at places that lie above such a cavity. Cavities below a flooring layer are a particular problem in the context of the installation of playable flooring layers, because those types of layers have only limited rigidity. Rather, those layers have to be elastic and resilient in order to protect the players from injury. Hence, an elastic sports flooring layer that is not fully supported by a solid base layer will bend downward into the cavity when pressure is applied to it. As a result, the sports flooring layer is stretched and contracts again whenever a ball or a player hits the layer on an area that is located above a cavity. The repeated stretching and contraction will cause accelerated material fatigue of the elastic sports flooring layer. Cracks and holes will develop in the elastic layer. These cracks may allow water to penetrate the layer and reach the base layer, thereby increasing the detrimental effect of repeated freeze-thaw cycles.

With the placement of an elastic layer on top of a leveled, compacted mixture of stones and elastic layers, this damage can be prevented because the granules and stones fill cavities in the base layer that may already exist in the base layer when the elastic layer is installed.

In a further beneficial aspect, the damage-inducing effect of freeze-thaw cycles is prevented because the compacted mixture of granules and stones provides more robust protection than solid materials like stone or concrete against damage that is caused by the expansion of frozen water. This is because the mixture of stones and elastic granules comprises air cavities that allow water that may have reached the base layer to expand into these cavities in the stone/elastic-granules mixture forming the substrate layer. Hence, the application of the stone/elastic-granules mixture does not only fill existing holes, but it also prevents the generation of new cavities as an effect of multiple freeze-thaw cycles.

In a further beneficial aspect, even in case frequent freeze-thaw cycles should once have generated a cavity in the base layer, mechanical damage and material fatigue may still be prevented because, in this case, some of the stones and/or granules of the substrate layer may penetrate into the cavity and fill it up, thereby maintaining the mechanical support below the elastic layer.

The use of elastic granules in the mixture may be advantageous because elastic granules, when compacted, have a tendency to regain their original size and shape. As a consequence, they exert pressure on other objects (stones, other elastic granules) in their neighborhood, thereby preserving the position of the stones and granules in the compacted substrate layer. Thereby, the elastic granules also preserve the compact structure of the substrate layer even in the absence of a binder or an adhesive. This may be beneficial because the absence of a binder or an adhesive in the substrate layer may ensure that the substrate layer comprises many cavities filled with air that allow any water that may have reached the contact zone between the base layer and the substrate layer to expand into these cavities without causing damage in the base layer.

In a further beneficial aspect, the use of elastic granules in the mixture may increase the elasticity of the overall surface structure, thereby offering the players better protection from injury.

According to embodiments, the base layer is a concrete, soil, sand, wood, or stone layer or a layer comprising a mixture of two or more of said materials. In particular, the base layer is a solid material, e.g., stone or concrete. Solid material, in particular porous, rigid material, has been observed to be particularly prone to freeze-thaw-cycle-induced damage. Applying the substrate mixture onto this type of base layer may hence protect the elastic layer from material fatigue that might likely be observable after some years of use if the elastic layer were directly installed on top of the base layer.

According to embodiments, the elastic granules are rubber granules, in particular ethylene propylene diene monomer (EPDM) rubber granules or styrene-butadiene rubber (SBR) granules.

This may be beneficial because the elasticity provided by the rubber granules protects the joints of the players from injury. In addition, the increased elasticity of the ground allows the ball to bounce back higher and faster. Furthermore, rubber is a cheap material that can be processed and granulized easily.

According to embodiments, the substrate mixture is free of a binder.

According to embodiments, the substrate mixture and the substrate layer are free of any adhesive fixing the stones and rubber granules.

The absence of a binder and/or another form of adhesive may be beneficial because this may ensure that in case a cavity has formed in the base layer as the result of frequent freeze-thaw cycles, this cavity is filled automatically, as in this case, some of the stones and/or granules of the substrate layer may penetrate into the cavity and fill it up, thereby maintaining the mechanical support below the elastic layer. For example, the elasticity and resilience of the elastic granules can be chosen such that all stones and elastic granules are fixed in the respective positions these objects acquired during the compaction process even if a cavity forms in the base layer. However, when an object (e.g., a ball or a player) hits the sports floor at an area above this cavity, some stones or elastic granules on the lower side of the substrate layer may be released by the impact from the substrate layer and may fall into and fill up the cavity in the base layer.

According to embodiments, at least 5%, preferably at least 10%, e.g., at least 20%, preferably 5-35%, of the volume of the compacted substrate layer consists of air-filled cavities between the stones and the elastic granules.

This may be beneficial because these cavities in the substrate layer make this layer robust against freeze-thaw-cycle-induced damage, as water that expands in the freezing process may fill the air-filled cavities without damaging the material or structure of the substrate layer. This is because air can easily be compressed and can then expand. The air-filled cavities in the substrate layer may also protect the surface of the base layer from freeze-thaw-cycle-induced damage because water that should have reached the contact zone of the base layer and the substrate layer may expand into these cavities when it freezes.

According to embodiments, the compacting comprises applying pressure on the applied mixture of the stones and elastic granules such that the elastic granules become deformed and the resilience of the deformed elastic granules fixes the stones and other elastic granules in their local environment even in the absence of a binder or an adhesive.

According to embodiments, the elastic layer is a polyurethane (PU) layer.

According to embodiments, the elastic layer or one of the other additional layers is an artificial turf layer or a hybrid turf layer.

Artificial turf or artificial grass is surface that is made up of fibers and is used to replace real grass. The structure of the artificial turf is designed such that the artificial turf has an appearance that resembles grass. Typically, artificial turf is used as a surface for sports such as soccer, football, rugby, tennis, and golf and for playing fields and exercise fields. Furthermore, artificial turf is frequently used for landscaping applications.

According to embodiments, at least one of the additional layers is a sealing layer adapted to prevent water from penetrating the playing surface and reaching the base layer.

According to embodiments, the two or more additional layers comprise at least two elastic layers, each of the elastic layers having different elastic-deformation characteristics (elastic deformability characteristics). The elastic deformation is highest in the topmost of the at least two elastic layers and is lowest in the lowest of the at least two elastic layers. For example, the elastic-deformation characteristics can be reduced 10% per layer in downward direction (i.e., in the direction toward the base layer). For example, each elastic layer can be a foamed or non-foamed polyurethane (PU) layer that may optionally comprise elastic granules, e.g., rubber granules. By varying the type of the PU, the degree of foaming and/or the amount of elastic granules within an elastic layer, it is possible to manufacture an elastic layer having precisely the desired degree of elastic deformation.

According to embodiments, the height of each elastic layer is at least 6 mm, preferably at least 9 mm. However, the height of the e-layer may depend on the intended use of the floor structure comprising the e-layer. For example, the height of an elastic layer used as support mat of an artificial turf that is to be used for soccer is preferably about 20 mm to 35 mm. To the contrary, the height of an elastic layer that is used as a support mat for an artificial turf that is to be used for a golf course is preferably about 10 mm-15 mm.

According to embodiments of the invention, the height of each of the one or more elastic layers is in the range of 8 mm-40 mm, in particular 10-35 mm, in particular 20-35 mm.

According to embodiments, the size distribution of the stones is an RRSB (Rosin, Rammler, Sperling, Bennet) distribution. In addition, or alternatively, the size distribution of the rubber granules is an RRSB distribution. For example, the stones and/or the rubber granulate can be obtained in a grinding process in a mill, whereby the mill is configured and filled in such a way that the grinding material itself acts as a grinding media. This size distribution can be advantageous as it may lead to a mixture of rubber particles and/or stones in which the particles are present in a comparatively stable package. Such a packing of the articles may largely prevent a lateral displacement of the particles, e.g. when mechanical forces hit the surface.

According to embodiments, the stones have a diameter of below 2.0 cm.

According to embodiments, the rubber granules have a diameter of below 2.0 cm.

According to embodiments, the substrate mixture consists of about 40-60 weight percent stones, the rest is the rubber granulate. The share of the rubber granules and the stones may be adapted in accordance with the respective requirements, e.g. in dependence on the type of sport or the thickness of the e-layer.

According to embodiments, the compacted, leveled substrate mixture has a height of at least 7.5 cm, preferably in the range of 7.5-15 cm.

According to embodiments, the rubber granules are PU-coated granules.

This may be beneficial, because PU is an elastic material whose elasticity can be tightly controlled by choosing appropriate types and amounts of PU-reaction educts (e.g., polyols, isocyanates, prepolymers), reaction conditions, and/or catalysts. By coating the elastic rubber granules with one or more PU layers, the elasticity of the granules can be increased and/or tightly controlled, thereby also increasing and tightly controlling the resilience of the coated elastic granules and their ability to firmly fix other objects in their environment as a result of the compaction step.

According to embodiments, the substrate mixture is applied such that the stones and the elastic granules are homogeneously mixed when they are applied on the base layer.

This may be beneficial, as it may ensure that the substrate layer in every one of its subregions approximately comprises the same number of elastic granules that keeps all objects in their environment in place as a result of the compaction. Hence, the mechanical “grip” of the individual objects in the substrate layer is homogeneously distributed in the substrate layer.

According to embodiments, the material of the base layer is susceptible for freeze-thaw-cycle-induced damages and is in particular a porous stone or a porous concrete material.

In a further aspect, the invention relates to a playing surface, in particular a sports floor or playing field. The playing surface comprises a substrate layer and one or more additional layers. The substrate layer lies on top of a base layer. The substrate layer is a leveled, compacted mixture of elastic granules and stones. The one or more additional layers lie on top of the substrate layer. At least one of the additional layers is an elastic layer. The substrate layer and the one or more additional layers form the playing surface.

According to embodiments, the playing surface is manufactured in accordance with a method according to any one of the examples and embodiments presented herein. Hence, any feature of the playing surface or the substrate mixture mentioned in the context of the method likewise applies to respective elements of the playing surface.

A “sports floor” as used herein is any type of floor that is suited for doing sports. In particular, a sports floor is a floor sufficiently elastic to protect the players from injuries. The sports floor can also be referred to and covers “sports flooring” and “sports surface.” Examples of sports floors are running tracks, tennis courts, artificial turf, etc.

A “playground floor” as used herein is any type of floor or flooring that is used as ground in a playground. A playground (also “playpark” or “play area”) is a place specifically designed to enable humans, in particular children, to play there. It is typically outdoors. While a playground is usually designed for children, some target other age groups. Common in modern playgrounds are play structures that link many different pieces of equipment.

A “sealing layer” as used herein is a layer that is basically impermeable by water. For example, the sealing layer can be a latex resin or an acrylic resin that can be used as the topmost layer, e.g., a coating layer, of a playing surface structure. The sealing layer prevents water from penetrating the playing surface, thereby increasing the robustness of the playing surface against freeze-thaw-cycle-induced damages.

The term “elasticity” as used herein refers to the ability of a material to recover its original dimensions and to return to its original shape after being subjected to stress. Solid objects will deform when adequate forces are applied to them. If the material is elastic, the object will return to its initial shape and size when these forces are removed. An “elastic layer” or “e-layer” is a layer made of an elastic material.

Preferably, the elastic layer is an area-elastic layer. The elastic layer can be, for example, a self-leveling, in-situ created layer composed of an elastic granulate, a binder, and additional substances. Alternatively, the elastic layer can be a layer of elastic tiles, e.g., PU tiles, made in a factory.

According to embodiments, the e-layer is adapted for use as a sports field or playground. According to embodiments, the e-layer has mechanical parameter values, e.g., in respect to shock absorption capacity, rigidity, and/or elasticity, which are adapted for protecting players from injuries when using the floor comprising the e-layer as a sports field or playground. Preferably, the e-layer has mechanical parameter values adapted for protecting players from injuries even if the sports field or playground does not comprise any additional elastic layers or an elastic substrate, meaning that the e-layer is basically the only layer adapted to protect the players from injuries. The sports field can be selected from a group comprising a baseball field, a tennis court, a handball court, a hockey field, a running track, and a football field.

According to embodiments, the e-layer has a shock absorption (measured at 23° C.) of at least 55%, preferably at least 65%. For example, the e-layer has a shock absorption of 55-70%. The shock absorption can be measured in accordance with the testing method detailed in the FIFA Handbook of Tests Methods for Football Turf 2015 (in particular Sections 4 and 11).

According to embodiments, the e-layer has a vertical deformation of 4 mm-11 mm as a result of an impact of a 20 kg mass measured at 23° C. in accordance with the testing method detailed in the “FIFA Handbook of Tests Methods for Football Turf 2015.”

An e-layer can be, for example, a layer that has a shock absorption (measured at 23° C.) of at least 55% and a vertical deformation of at least 4 mm, preferably at least 6 mm, measured at 23° C. in accordance with the testing method detailed in the FIFA Handbook of Tests Methods for Football Turf 2015.

According to one embodiment, the e-layer is a layer that has a head injury criteria (HIC) of less than 1,000. For example, this type of e-layer can be used as a rugby sports floor. According to some embodiments, the e-layer is a layer that has a HIC of less than 200. For example, this type of e-layer can be used as a playground. The testing for the HIC value of a surface or layer and for the related critical height of said surface or layer is typically done in a laboratory; however, testing may also be done in the field using the F1292 testing methodology. The ASTM International (ASTM) Standard F1292 is designed to provide a testing method for surfacing materials that will allow assessment of impact attenuation of playground surfacing and thus reduce the severity and frequency of fall-related head injuries. The shock or force of the impact of an object on a surface can be measured in “g's,” which is the acceleration due to gravity. The maximum peak deceleration before a debilitating head injury might occur is 200 g's. HIC measures the time of deceleration. The value of the HIC must be less than 1,000 to avoid a life-threatening head injury. A “critical height” of a surface is a physical property of a surface or layer that is defined as the maximum fall height from which a life-threatening head injury would not be expected to occur. “Fall height” is defined as the vertical distance between a designated play surface and the playground surface beneath it. Fall heights of various kinds of play equipment are identified in the U.S. Consumer Product Safety Commission (CPSC) publication “Public Playground Safety Handbook” in Section 5 under each type of equipment. Critical height is determined by a combined measurement of acceleration (shock) of an impact and the duration of the impact as it relates to head injury.

It is understood that one or more of the aforementioned embodiments of the invention may be combined as long as the combined embodiments are not mutually exclusive.

BRIEF DESCRIPTION OF THE DRAWINGS

The following embodiments of the invention are explained in greater detail, by way of example only, making reference to the drawings:

FIG. 1 is a schematic, a cross-sectional view of a state-of-the-art playing surface.

FIG. 2 is a flow chart of a method of manufacturing a playing surface.

FIG. 3 is a schematic, cross-sectional view of a playable structure comprising a leveled, compacted mixture of stones and elastic granules.

FIG. 4 is a schematic, cross-sectional view of a pavement structure at several moments during the manufacturing of the playing surface.

FIG. 5 is a schematic, cross-sectional view of a playable structure comprising an artificial turf layer.

FIG. 6 is a schematic, cross-sectional view of a playable structure comprising a sealing layer.

DETAILED DESCRIPTION

Like-numbered elements in these figures either are equivalent elements or perform the same function. Elements that have been discussed previously will not necessarily be discussed in later figures if the function is equivalent.

FIG. 1 is a schematic, a cross-sectional view of a state-of-the-art playing surface as it may look after several years of use in an area with frequent freeze-thaw cycles. An elastic layer 102 has been placed on top of a base layer 104, e.g., a concrete base. The base layer may originally have had a plain, level surface that provided mechanical support for the elastic layer 102 over its full extent. However, after many years in a region with many freeze-thaw cycles, the surface of the base layer may comprise multiple depressions and cracks. As a consequence, some regions of the elastic layer are not mechanically supported by the base layer and will be stretched strongly if a heavy object hits the elastic layer in said regions. This stretching may soon result in material fatigue and a significantly shortened life expectancy of the sports floor. In particular, if the stretching of the elastic layer 102 results in the elastic layer becoming brittle and water-permeable, the decay of the elastic layer may be accelerated because even more water may reach and further damage the base layer.

FIG. 2 is a flow chart of a method of manufacturing a playing surface 300, 400, 500, 600, e.g., a sports field or playground as depicted, for example, in FIGS. 3, 4, 5, and 6. The playing surface generated with this method may be particularly robust against freeze-thaw-cycle-induced damages. In the following, the method of FIG. 2 will be described by making reference also to elements of FIGS. 3 and 4.

The method comprises a first step 202 of providing a substrate mixture 402. The substrate mixture comprises elastic granules 304 and stones 306 as depicted, for example, in FIGS. 3 and 4. The provision of the mixture can imply, for example, that an installer in the immediate vicinity of the place where the sports floor is to be installed mixes stones and elastic granulate in the desired ratio. Mixing can be done manually. Preferably, however, mixing is done in a rotating drum, which can take larger volumes of stones and elastic granulate and mix them homogeneously. For example, mortar mixers or construction vehicles and/or equipment of different sizes can be used to produce a homogeneous mixture of elastic granulate and stones. The amount of the mixture to be produced depends on the size of the area onto which the mixture is to be applied and on the desired thickness of the substrate layer 302. The choice of a suitable mixing device depends on the mixing capacity required in view of the quantity of mixture required. Since the mixture preferably does not contain any binding agents or adhesives but rather is a loose composition of particles, smaller mixing containers can in principle also be used to gradually provide the desired quantity of the mixture. There is no particular time pressure with regard to the processing and application of the mixture on the base layer 310, as the mixture preferably does not contain any binder or adhesive with a limited time window for processing until curing that would have to be taken into account.

Alternatively, the mixture 402 can also be produced in a factory and then transported in sacks or loose on a truck to where the new sports floor is to be created.

Next, in step 204, the substrate mixture is applied on a base layer 310. This step can be performed manually, automatically, or semi-automatically. For example, a mortar mixer can tip the finished, homogeneous mixture onto the area specified above. Alternatively, a technician can also apply the mixture from a bucket.

Next, in step 206 of the method, the applied mixture is leveled. For example, a person with a long rod or a rake can smooth out the mixture that has been applied to the base layer and thus make it flat and level. It is also possible for a machine, such as a mortar mixer, to travel in several lanes over the base layer, thereby applying a defined amount of the mixture to the base layer, whereby an elongated object (rod, rake, knife) in tow smooths and levels the applied mixture.

Next, in step 208, the leveled substrate mixture 402 is compacted. The compacting is performed such that the leveled substrate mixture 402 forms a compact substrate layer 302. Compaction is a process that reduces the pore space of a surface layer filled with air or other volatile materials. This gives the substrate layer a desired property; it becomes more resistant to mechanical stresses and has increased stability and ability to keep all objects contained in this layer at a constant position due to the resilience of the elastic granules in this layer. For example, compaction of the mixture 402 can be performed with vibratory or oscillating rollers, whereby the interaction of vibrations of the roller drum and the weight of the roller transform the loose stone/elastic granule mixture 402 into a compacted substrate layer 302. The intensity of compaction can be controlled, e.g., by the deflection of the drum; i.e., the amplitude of the vibration, the frequency of the vibration; i.e. the frequency and the impact time; i.e. the travel speed. For example, a single-drum compactor with padfoot drums for large amplitudes can be used.

The leveling step can in some embodiments be performed together or in combination with step 204, 208, or both.

For example, a first vehicle may comprise a rotatable container in which the mixture 402 is homogeneously mixed. While the first vehicle moves over the base layer 310, a defined amount of the mixture 402 is released and applied to the ground and an elongated object in tow of the first vehicle immediately levels the applied mixture. The first vehicle is followed by a second vehicle comprising vibratory or oscillating rollers that compact the leveled mixture.

According to another example, a first vehicle or a person may apply the mixture on the base layer while moving over the base layer. The applied mixture is not leveled at first. Then, a compaction machine or a compaction device is used for compacting the mixture. The compaction can be performed in lanes, whereby the compacted lanes overlap in order to ensure that the compacted mixture is level. In this case, the compaction step may inherently comprise a leveling step, because the applied mixture is compacted and leveled in a single operation.

Next in step 210, one or more additional layers 502, 308, and 602 are applied on top of the substrate layer. At least one of the additional layers is an elastic layer 308 that is sufficiently elastic to protect the players from injuries. Depending on the embodiment, multiple elastic layers may be applied. The additional layers may comprise various types of structurally and functionally diverse layers, depending on the particular use case scenario. For example, one of the additional layers can be an artificial turf layer, a sealing layer, a pigmented coating layer for providing a desired color impression, an adhesive layer in between two of the additional layers, barrier layers, and the like.

Any one of the additional layers, for example, may be simply placed on top of the existing layers without applying an adhesive layer. Alternatively, the additional layer can be glued to or mechanically fixed to the existing layers.

When all desired additional layers have been applied, the substrate layer in combination with one or more additional layers forms the playing surface.

FIG. 3 is a schematic, cross-sectional view of a playable structure 300 comprising a leveled, compacted mixture of stones 306 and elastic granules 304 that provides the substrate layer 310. FIG. 3 shows that the compacted mixture compensates for irregularities and depressions in the base layer 310. On the one hand, this may be due to the fact that these irregularities may already have existed when the mixture of stone and elastic granules was applied to the base layer and then compacted. On the other hand, this effect can also be the result of the compacted substrate layer in some designs losing some of the stones and the elastic granules at the points where the base layer shows damage and gaps so that these can fill the cavities created in the base layer. Hence, the substrate layer may be adapted to repair itself and the base layer automatically.

FIG. 4 is a schematic, cross-sectional view of a surface structure at three different moments during the manufacturing of the playing surface 400.

FIG. 4A shows a first state 410 of a surface structure after a loose mixture 402 of stones 306 and elastic granules 304 has been applied to a base layer 310. The surface of the base layer has holes and depressions, but these are completely filled by the stones and the elastic granules. FIG. 4A shows an essentially level but not-yet-compacted layer.

FIG. 4B shows a second state 420 of the surface structure depicted in FIG. 4A after the mixture 402 has been compacted, for example, by a roller. The stones and elastic granules are now visibly more densely packed and form the substrate layer 302. However, the substrate layer still contains air-filled cavities.

FIG. 4C shows a simple example of a complete playing surface structure 400 after an elastic layer 308 has been applied to the substrate layer 302. The playing surface 400 can be, for example, a sports floor, a playground floor, or a floor of a recreational facility.

Optionally, there may be an adhesive layer between the substrate layer and the elastic layer 308 (not shown), but this adhesive layer preferably does not penetrate the substrate layer 302 at all or only very slightly.

The base layer can be, for example, soil, sand, concrete, stones, or mixtures thereof. The base layer can likewise be wood or an existing floor pavement. The base layer is preferably an outdoor base layer.

The height of the e-layer 308 depends on the intended use. Typically, the height of the e-layer is in the range of 8 mm-40 mm.

The e-layer can be applied in situ (e.g., by generating a liquid PU reaction mixture optionally comprising elastic granules before the liquid mixture is applied on the substrate layer. The liquid mixture has self-leveling capabilities and may optionally be leveled actively with the help of a leveling device. The liquid reaction mixture has a viscosity and/or reaction speed that ensures that the liquid PU reaction mixture will not, or at least will not deeply, penetrate the substrate layer. For example, the PU reaction mixture may be adapted to harden before the mixture penetrates the upper 0.8 cm of the substrate layer, preferably before it penetrates the upper 0.2 cm of the substrate layer.

Alternatively, the e-layer is manufactured at a manufacturing plant (e.g., in the form of e-layer rolls or tiles). The rolls or tiles are transported to the use site and laid on the substrate layer of that use site. Optionally, the e-layer tracks generated by the e-layer rolls and/or the e-layer tiles are attached to the substrate layer. For example, the e-layer roll or the e-layer tiles are glued, tacked, nailed, or otherwise fixed to the base layer, thereby preventing the filling of the air cavities of the substrate layer.

Preferably, the additional layer that is applied directly on top of the substrate layer is applied without any adhesive layer in between the substrate layer and said additional layer. Alternatively, said additional layer can comprise an adhesive layer or coating on its lower side that contacts the substrate layer. In this case, however, the adhesive layer or coating is highly viscous such that it does not penetrate the compacted substrate layer deeper than a maximum penetration depth. The maximum penetration depth is, according to embodiments, 0.8 cm, preferably 0.4 cm. This may ensure that the substrate layer remains basically free of any binder or adhesive that can prevent the granules and stones from sliding into depressions in the soil that may later develop as a result of the weather.

FIG. 5 is a schematic, cross-sectional view of a playable structure 500 comprising an artificial turf layer 502. The playable structure 500 is an example for a playable structure according to embodiments of the invention that comprises more than one additional layer. Any of the one or more additional layers can simply be put onto the respective lower layer without any fixation means. Alternatively, any of the one or more additional layers is glued, nailed, tacked, or otherwise fixed onto the respective lower layer.

FIG. 6 is a schematic, cross-sectional view of a playable structure 600 comprising a sealing layer 602. The playable structure 600 is an example for a playable structure according to embodiments of the invention that comprises more than one additional layer. In this case, the structure 600 comprises the elastic layer 308 as a first additional layer and the sealing layer 602 as a second additional layer.

LIST OF REFERENCE NUMERALS

-   -   102 sports floor     -   104 ground, base layer     -   106 cavity (cracks, depressions of base layer)     -   202-210 steps     -   300 playing surface     -   302 compacted mixture of stones and elastic granules     -   304 elastic granules     -   306 stones     -   308 elastic layer     -   310 base layer     -   400 playing surface     -   402 (non-compacted) stone/elastic granules mixture     -   410 surface structure comprising a leveled stone/elastic         granules mixture     -   420 surface structure comprising a compressed stone/elastic         granules mixture     -   500 playing surface     -   502 artificial turf     -   600 playing surface     -   602 sealing layer 

1. A method for laying a playing surface, the playing surface being in particular a sports floor or playing field, the method comprising the steps of; providing a substrate mixture comprising elastic granules and stones; applying the substrate mixture on a base layer; leveling the applied substrate mixture; compacting the leveled substrate mixture such that a compact substrate layer is formed; and applying one or more additional layers on top of the substrate layer, at least one of the additional layers being an elastic layer, wherein the substrate layer and the one or more additional layers form the playing surface.
 2. A method for laying a playing surface that provides robust protection against freeze-thaw-cycle-induced damages, the playing surface being in particular a sports floor or playing field, the method comprising the steps of: providing substrate mixture comprising elastic granules and stones; applying the substrate mixture on a base layer, the base layer being located in a geographic area subjected to multiple freeze-thaw-cycles per year. leveling the applied substrate mixture; compacting the leveled substrate mixture such that a compact substrate layer is formed; and applying one or more additional layers on top of the substrate layer, at least one of the additional layers being an elastic layer, wherein the substrate layer and the one or more additional layers form the playing surface.
 3. The method according to claim 1, the base layer being a concrete, soil, sand, wood, or stone layer or a layer comprising a mixture of two or more of said materials.
 4. The method according claim 1, wherein the elastic granules are rubber granules, in particular EPDM or SBR rubber granules.
 5. The method according to claim 1, wherein the substrate mixture is free of a binder.
 6. The method according to claim 1, wherein the substrate mixture and the substrate layer are free of any adhesive fixing the stones and rubber granules.
 7. The method according to claim 1, wherein at least 5%, preferably at least 10%, e.g., at least 20% of the volume of the compacted substrate layer consists of air-filled cavities between the stones and the elastic granules.
 8. The method according to claim 1, wherein the elastic layer is a PU layer.
 9. The method according to claim 1, wherein the elastic layer or one of the other additional layers is an artificial turf layer or a hybrid turf layer.
 10. The method according to claim 1, wherein at least one of the additional layers is a sealing layer adapted to prevent water from penetrating the playing surface and reaching the base layer.
 11. The method according to claim 1, wherein the size distribution of the stones is an RRSB distribution and wherein the diameter of the stones is below 2.0 cm.
 12. The method according to claim 1, wherein 40-60% of the weight of the substrate mixture consists of the stones and the rest of the weight of the substrate mixture consists of the rubber granules.
 13. The method according to claim 1, wherein the size distribution of the rubber granules is an RRSB distribution and wherein the diameter of the rubber granules is below 2.0 cm.
 14. The method according to claim 1, wherein the rubber granules are PU-coated granules.
 15. The method according to claim 1, wherein the substrate mixture is applied such that the stones and the elastic granules are homogeneously mixed when they are applied on the base layer.
 16. The method according to claim 1, wherein the compacting comprises applying pressure on the applied mixture of the stones and elastic granules such that the elastic granules become deformed and the resilience of the deformed elastic granules fixes the stones and other elastic granules in their local environment also in the absence of a binder or an adhesive.
 17. The method according to claim 1, wherein the material of the base layer is susceptible to freeze-thaw-cycle-induced damages and is in particular a porous stone or a porous concrete material.
 18. A playing surface, in particular a sports floor or playing field, comprising: a substrate layer lying on top of a base layer, the substrate layer being a leveled, compacted mixture of elastic granules and stones; and one or more additional layers lying on top of the substrate layer, at least one of the additional layers being an elastic layer, wherein the substrate layer and the one or more additional layers form the playing surface. 